This invention relates to an emulsifier system which is suitable for the production of low-foaming oil-in-water emulsions in soft water. The emulsifier system may be combined with suitable carboxylic acids to create a corrosion protection system. The present invention also relates to a water-miscible emulsion concentrate containing oil and the present emulsifier system, and to ready-to-use oil-in-water emulsions prepared therefrom. Even in soft water, these emulsions exhibit only a slight tendency to foam and may be used for various industrial metal processing applications, for example as cleaning, corrosion protection or cooling lubricant emulsions.
Corrosion protection emulsions are used as passivating agents for temporarily protecting metallic workpieces from corrosive atmospheric influences. They essentially contain apolar or polar oils, emulsifiers, corrosion inhibitors and water. Conventional commercial systems are based on oil concentrates containing emulsifiers and corrosion inhibitors, but little or no water. The emulsifiers and corrosion inhibitors must thus be soluble in oil. In order to produce oil-in-water emulsions (xe2x80x9cO/W emulsionsxe2x80x9d) which are used in dilute form with water, such systems must be self-emulsifying.
Cooling lubricant emulsions, which are used for machining or forming metallic workpieces, have a similar composition to corrosion protection emulsions, as they must also exhibit a corrosion inhibiting action. Lubricating action may be improved by the addition of suitable lubricating additives.
A feature common to all these types of emulsion is that they have a tendency to foam due to the emulsifiers used. The tendency to foam is particularly pronounced if the emulsifier system contains anionic surfactants. In the event of use in hard water, the tendency to foam is decreased by the fact that the anionic surfactants may react with calcium ions to form sparingly soluble salts which have a foam inhibiting action. In soft to medium hardness water, i.e. in water having hardness of less than 12xc2x0 and in particular of less than 8xc2x0 dH [German hardness], such emulsions are unusable due to the increased tendency to foam, at least if they are used in spraying applications.
Emulsifier systems containing only nonionic emulsifiers are known from DE-A-39 33 137 and DE-A-43 23 908. The emulsifier system according to DE-A-39 33 137 consists of at least one addition product of 2 to 20 mol of ethylene oxide on fatty alcohols having 10 to 22 carbon atoms, to which may be added up to an identical number of parts, by weight, of a coemulsifier component consisting of at least one fatty alcohol having 12 to 22 carbon atoms. The emulsifier system according to DE-A-43 23 908 consists of at least one addition product of 5 to 12 mol of ethylene oxide on fatty alcohols having 16 to 18 carbon atoms and at least one addition product of 1 to 2 mol of ethylene oxide on fatty alcohols having 12 to 18 carbon atoms or at least one monoglycerol ester of fatty acids having 16 to 18 carbon atoms. The emulsion concentrates according to both these documents are produced using the so-called xe2x80x9cphase inversion processxe2x80x9d. Disadvantageous features in this connection include the relatively high water content of the emulsion concentrates, the elaborate production process and the low possible inhibitor content of the concentrates. Moreover, the emulsion stability of the concentrate itself must be optimised, so limiting the latitude possible in formulation.
An object of the present invention is to provide an emulsifier system with which low-water or anhydrous emulsion concentrates for O/W emulsions may be produced by simple stirring. The ready-to-use O/W emulsions obtainable from these concentrates by combination with water should also exhibit only a low tendency to foam even in soft water.
This object is achieved by a low-foam emulsifier system consisting of:
(a) ethoxylates/propoxylates of fatty alcohols having 8 to 18 carbon atoms in the alcohol with 2 to 6 ethylene oxide units and 4 to 8 propylene oxide units; and
(b) fatty alcohols and/or fatty alcohol propoxylates having 12 to 24 carbon atoms in the alcohol and 0 to 3 propylene oxide units and/or the distillation residue of these fatty alcohols;
in a ratio, by weight, of (a):(b) of 1:0.3 to 0.3:1.
Narrow limits are thus set on the composition of the emulsifier system and on the molecular structure of the emulsifiers used. On the one hand, according to (a) fatty alcohol ethoxylates/propoxylates bearing both 2 to 6 ethylene oxide units and 4 to 8 propylene oxide units must be present. These hydrophilising components must be combined with the more hydrophobic non-alkoxylated component (b) fatty alcohols having 12 to 24 carbon atoms, the distillation residue thereof or the alkoxylation products thereof containing an average of up to at most 3 propylene oxide units. It is also necessary to comply with the stated approximate ratio, by weight. The distillation residue of fatty alcohols containing 12 to 24 carbon atoms is obtainable as xe2x80x9cPernil(copyright) RUxe2x80x9d from Henkel KGaA, Dxc3xcsseldorf. Pernil(copyright) RU has been assigned CAS number 68603-17-8.
As described above, this emulsifier system may be formulated with further components to produce cleaning, corrosion protection and/or cooling lubricant emulsions. The emulsifier system may, however, be offered for sale as it is. The purchaser may then use it to prepare the desired type of emulsion. In a first stage, the emulsifier system may be formulated with a corrosion protection component, from which a concentrate for a corrosion protection emulsion may be produced by adding oil. According to a second embodiment, the present invention thus relates to a corrosion protection and emulsifier system consisting of:
15 to 40 parts, by weight, of one or more straight- or branched-carboxylic acids having 6 to 10 carbon atoms or the anions thereof; and
15 to 40 parts, by weight, of emulsifier component consisting of:
(a) ethoxylates/propoxylates of fatty alcohols having 8 to 18 carbon atoms in the alcohol with 2 to 6 ethylene oxide units and 4 to 8 propylene oxide units; and
(b) fatty alcohols and/or fatty alcohol propoxylates having 12 to 24 carbon atoms in the alcohol and 0 to 3 propylene oxide units and/or the distillation residue of these fatty alcohols;
in a ratio, by weight, of (a):(b) of 1:0.3 to 0.3:1.
Since corrosion protection emulsions conventionally have neutral to basic pH values, it is preferable to use the carboxylic acids at least in part in neutralised form, i.e. as salts. Suitable basic components for neutralisation are potassium hydroxide solution and/or alkanolamines, wherein the latter promote the corrosion inhibition action. Due to the risk of forming nitrosamines, it is less preferred to use dialkanolamines for this purpose. Instead, monoalkanolamines or trialkanolamines or, preferably, mixtures thereof are used. In particular, ethanolamines are used.
The carboxylic acids having a corrosion inhibiting action may be straight- or branched-chain.
Mixtures of different acids may be particularly advantageous. Preferred examples of such carboxylic acids are caprylic acid, ethylhexanoic acid, isononanoic acid and isodecanoic acid.
According to another embodiment, the present invention relates to a water-miscible emulsion concentrate containing oil and:
15 to 35 parts, by weight, of an oil component;
30 to 80 parts, by weight, of the corrosion protection and emulsifier system according to one or both of claims 2 and 3;
and, if desired, further auxiliary or active substances.
Such a concentrate may be obtained by adding the appropriate number of parts, by weight, of an oil component to the corrosion protection and emulsifier system described above. It is, of course, also possible to produce such a concentrate by mixing the oil component, the individual emulsifiers of the emulsifier system and the carboxylic acids in any desired sequence. The carboxylic acids may be used directly as salts. For processing reasons, however, it is more advantageous to mix the acids themselves into the other components and to neutralise them by adding alkali metal hydroxide solution, in particular potassium hydroxide solution, and/or alkanolamines only once they have been blended with the oil component and the emulsifier system.
Apolar or polar oils of a petrochemical or natural origin may be used as the oil component. Synthetic oil components are also suitable. Examples of usable oil components are paraffinic or naphthenic mineral oil, dialkyl ethers having 12 to 20 carbon atoms and/or ester oils. Optional further auxiliary or active substances which may be mentioned are: lubricating additives in general and in particular so-called xe2x80x9cextreme pressurexe2x80x9d additives (known as EP additives), further corrosion inhibitors, such as boric acid or additional alkanolamines, solubilising agents, such as glycols, glycerol or Na cumene sulfonate. Biocides, which extend the service life of the emulsion, may also be added.
The present invention also relates to the ready-to-use oil-in-water emulsion obtainable by combining about 0.5 to about 10 parts, by weight, of the concentrate described above with about 99.5 to about 90 parts, by weight, of water. By virtue of the self-emulsifying characteristics of the emulsion concentrate, the ready-to-use emulsion forms on combination with water spontaneously or after slight mechanical agitation, such as stirring. This emulsion may be used, for example, as a cleaning, corrosion protection or cooling lubricant emulsion. When soft water is used for preparation, the emulsion exhibits the major advantage over prior art emulsions that it has only a slight tendency to foam. The emulsion may thus be used in spray processing within the range of temperatures between the freezing point and the boiling point of the emulsion and requires no minimum temperature for spraying applications. The low foaming characteristics are also noticeable in applications as a cooling lubricant emulsion. Although the novel emulsifier system and the emulsions containing it in particular exhibit their advantages in soft water, they may, however, also be used in hard water without disadvantage.